Well, between Planet Zebes, Brinstar, Brinstar Depths and Norfair, I'd forgive someone for thinking lava was an emphasis of the series.
Plus there's the infamous Varia suit authorization thing in Other M that even the vaguest of Metroid enthusiasts know about. That centers around lava too.
I've honestly yet to see someone who has crafted their own image of Metroid based solely around the lava stages in Smash. Pretty sure most people's idea is that it's about a bounty hunter in space (that was my first impression after being exposed to Metroid for the first time in Smash 64). I'll consider it a problem if if the general public's view on the franchise starts matching that notion.
Certainly no stereotype, but I'd agree that there's been a lack of variation in the Metroid stages. If I weren't already a fan, there'd be little in Smash outside of Brinstar Depths to show me the scope of Samus's adventures. Really surprised Phaaze or the Artifact Temple didn't make it in over Orpheon. SR388 would be nice, too
The whole scope of a game will never be accurately represented with a few stages in a fighting game, even with the devs' best intentions in my mind for those particular franchises. There are just too many climatic moments and memorable set pieces that it would be a logistical nightmare trying to do them all justice.
I know that Pokemon games have more than two Stadiums and two Leagues. I know that Mario has more than just Mushroom Kingdom. I know that the Legend of Zelda is more than a tall structure overlooking Hyrule. I know Metal Gear has more landscapes other than Shadow Moses. Or that Kirby isn't just in Dreamland. I know that DK has more set pieces than jungles. But a lot of these franchises also follow certain aesthetic themes for their presentations. A theme that is also tied to the earliest levels of a game, therefore everyone who plays it is bound to remember them regardless if they finish the game or not. So it's no wonder why most stages tend to be reflected off the starting points of those games: Kongo Jungle, Jungle Japes, Mushroom Kingdom, Peach's Castle, Green Greens, Brinstar, Corneria, Brigate Orpheon, Green Hill Zone, Umbra Clock Tower, Midgar, Skyloft. Luigi's Mansion, Delfino Plaza, Yoshi's Story, both Yoshi's Islands, both Mute Cities, Jungle Hijinx, Dreamland, etc.
For the record, I genuinely don't understand the support for Phendrana Drifts. First, ice stages aren't hugely popular because of their physics. Second, what part of Phendrana specifically? Third, ice stages aren't unique to Metroid. Mario, Kirby, DK, Pokemon and Zelda feature them prominently in most of their games. I rarely think of ice stages when I think Metroid, so better take them from Ice Climber because ice is their whole shtick, or add Homecoming Hijynx because that was the theme for DK Tropical Freeze. I would rather advocate for the flagship Olympus from Corruption during the space pirate assault. SR388 would be a tough one because the areas of that game have a thematic issue. Perhaps set it around one of the Chozo gates and have poison on both sides (hey, it's not lava nor acid).
Never understood the issue with Orpheon. It's a space station, and Samus tends to visit lots of those. That place teaches you to play the game and kickstarts her adventure in Prime. And I don't mind Brinstar Depths because the lava isn't part of the stage's gameplay and because it features iconic villain Kraid turning the stage around, which is a rather unique feature and one of the series' best tunes. That stage actually left an impression in me because it showed that there was a cool looking Godzilla-esque monster that I would have to fight.